As is known in the art, a coupling member is used to install a toilet seat device with warm-water sprays at a rear portion of a toilet bowl. The coupling member is inserted in a mounting hole formed at the rear portion of the toilet bowl. A wide variety of coupling members are provided as the coupling member. A coupling member for a toilet seat device with warm-water sprays is disclosed in a Patent document No. 1, for example, in which it has a good workability since it is operated only from an upper side of the toilet bowl.
That is, the coupling member for the toilet seat device with warm-water sprays disclosed in the Patent document No. 1 has a circular cylindrically-shaped elastic deforming portion that is inserted into a mounting hole formed at a rear portion of a toilet bowl, a bolt that is inserted into the circular cylindrically-shaped elastic deforming portion and that has a threaded portion along an entire length thereof except a head portion, and a nut that is provided on the circular cylindrically-shaped elastic deforming portion, screwed on the threaded portion, and moved upward by rotational operation in one direction from an upper side of the bolt so as to enlarge the circular cylindrically-shaped elastic deforming portion in a circumferential direction. In such coupling member for the toilet seat device with warm-water sprays, if the nut is moved upward by the rotational operation in one direction from the upper side of the bolt, the circular cylindrically-shaped elastic deforming portion is enlarged in the circumferential direction. Then, when the circular cylindrically-shaped elastic deforming portion enlarged in the circumferential direction is strongly and firmly held between the nut and an inner wall of the mounting hole of the toilet bowl, the toilet seat device with warm-water sprays located at the side of the coupling member is indirectly and detachably fixed on the toilet bowl.    PATENT DOCUMENT No. 1: Japanese Laid Open Utility Model Publication No. Shou-62-72372